Editor's note: Thursday marked two years since Japan's security-related laws came into force. How can Japan deal with North Korea, which has continued with its nuclear and missile development, and China, whose maritime advances are becoming increasingly assertive? This is the first installment of a series examining the key defense challenges facing Japan. ___ TOKYO — In November 2017, a B-1 strategic bomber of the U.S. Air Force took off from Andersen Air Force Base in the U.S. territory of Guam and flew above the Pacific Ocean to airspace near the Kyushu region. There, F-15 fighter jets from Japan's Air Self-Defense Force joined the B-1 bomber in mid-flight. As the B-1 flew toward the Korean Peninsula, the F-15s occasionally flew close to the bomber; at other times, they kept their distance while staying vigilant for suspicious aircraft that might approach the bomber. Thi...